A magnetic resonance imaging (MRI) apparatus is an imaging apparatus which excites nuclear spins in a patient placed in a static magnetic field with a radio frequency (RF) signal of Larmor frequency and thereby generates an image by reconstructing a magnetic resonance signal generated from the patient as a result of the excitation. Unlike medical image generating apparatus which uses X-rays, the MRI apparatus does not cause radiation exposure, and thus has spread in medical scenes as an apparatus capable of low-invasive diagnostic imaging.
In the field of MRI, a technique is available which can obtain information about a four-dimensional three-directional velocity vector made up of three spatial dimensions and multiple time phases. This field is generally known as 4D Flow. 4D Flow uses a technique which is called a phase contrast method and is capable of measuring flow velocity as a phase, and blood flow information can be obtained non-invasively from data provided by 4D Flow.
Flow velocity, flow rate, and, wall shear stress (WSS) can be found from the data provided by 4D Flow. A conventional technique obtains vascular information from intensity images provided by 4D Flow and images obtained by a separate scan and uses vascular information for WSS calculation.
WSS heavily depends on vascular information, i.e., extraction accuracy of a vascular wall region. However, in the conventional technique, four-dimensional image data which is provided by 4D Flow and can be used to calculate four-dimensional velocity vector data has a low spatial resolution, making it difficult to find a correct vascular wall region from the image data.
Also, changes in the vascular wall region caused by cardiac cycles cannot be drawn from high-resolution image data obtained by scanning separately from 4D Flow according the conventional technique, which results in reduced calculation accuracy of WSS.
One of problems to be solved by the present invention is to provide a medical image processing apparatus and a medical image processing method which can improve calculation accuracy of WSS.